﻿using System;
using System.Diagnostics;
using System.Text;

// CHECKSTYLE:OFF
/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

namespace pili_sdk_csharp.pili_common
{

    /// <summary>
    /// Utilities for encoding and decoding the Base64 representation of
    /// binary data.  See RFCs <a
    /// href="http://www.ietf.org/rfc/rfc2045.txt">2045</a> and <a
    /// href="http://www.ietf.org/rfc/rfc3548.txt">3548</a>.
    /// </summary>
    public sealed class Base64
    {
        /// <summary>
        /// Default values for encoder/decoder flags.
        /// </summary>
        public const int DEFAULT = 0;

        /// <summary>
        /// Encoder flag bit to omit the padding '=' characters at the end
        /// of the output (if any).
        /// </summary>
        public const int NO_PADDING = 1;

        /// <summary>
        /// Encoder flag bit to omit all line terminators (i.e., the output
        /// will be on one long line).
        /// </summary>
        public const int NO_WRAP = 2;

        /// <summary>
        /// Encoder flag bit to indicate lines should be terminated with a
        /// CRLF pair instead of just an LF.  Has no effect if {@code
        /// NO_WRAP} is specified as well.
        /// </summary>
        public const int CRLF = 4;

        /// <summary>
        /// Encoder/decoder flag bit to indicate using the "URL and
        /// filename safe" variant of Base64 (see RFC 3548 section 4) where
        /// {@code -} and {@code _} are used in place of {@code +} and
        /// {@code /}.
        /// </summary>
        public const int URL_SAFE = 8;

        /// <summary>
        /// Flag to pass to indicate that it
        /// should not close the output stream it is wrapping when it
        /// itself is closed.
        /// </summary>
        public const int NO_CLOSE = 16;

        //  --------------------------------------------------------
        //  shared code
        //  --------------------------------------------------------

        private Base64()
        {
        } // don't instantiate

        //  --------------------------------------------------------
        //  decoding
        //  --------------------------------------------------------

        /// <summary>
        /// Decode the Base64-encoded data in input and return the data in
        /// a new byte array.
        /// <p/>
        /// <para>The padding '=' characters at the end are considered optional, but
        /// if any are present, there must be the correct number of them.
        /// 
        /// </para>
        /// </summary>
        /// <param name="str">   the input String to decode, which is converted to
        ///              bytes using the default charset </param>
        /// <param name="flags"> controls certain features of the decoded output.
        ///              Pass {@code DEFAULT} to decode standard Base64. </param>
        /// <exception cref="IllegalArgumentException"> if the input contains
        ///                                  incorrect padding </exception>
        public static byte[] decode(string str, int flags)
        {
            return decode(System.Text.Encoding.UTF8.GetBytes(str), flags);
        }

        /// <summary>
        /// Decode the Base64-encoded data in input and return the data in
        /// a new byte array.
        /// <p/>
        /// <para>The padding '=' characters at the end are considered optional, but
        /// if any are present, there must be the correct number of them.
        /// 
        /// </para>
        /// </summary>
        /// <param name="input"> the input array to decode </param>
        /// <param name="flags"> controls certain features of the decoded output.
        ///              Pass {@code DEFAULT} to decode standard Base64. </param>
        /// <exception cref="IllegalArgumentException"> if the input contains
        ///                                  incorrect padding </exception>
        public static byte[] decode(byte[] input, int flags)
        {
            return decode(input, 0, input.Length, flags);
        }

        /// <summary>
        /// Decode the Base64-encoded data in input and return the data in
        /// a new byte array.
        /// <p/>
        /// <para>The padding '=' characters at the end are considered optional, but
        /// if any are present, there must be the correct number of them.
        /// 
        /// </para>
        /// </summary>
        /// <param name="input">  the data to decode </param>
        /// <param name="offset"> the position within the input array at which to start </param>
        /// <param name="len">    the number of bytes of input to decode </param>
        /// <param name="flags">  controls certain features of the decoded output.
        ///               Pass {@code DEFAULT} to decode standard Base64. </param>
        /// <exception cref="IllegalArgumentException"> if the input contains
        ///                                  incorrect padding </exception>
        public static byte[] decode(byte[] input, int offset, int len, int flags)
        {
            // Allocate space for the most data the input could represent.
            // (It could contain less if it contains whitespace, etc.)
            Decoder decoder = new Decoder(flags, new byte[len * 3 / 4]);

            if (!decoder.process(input, offset, len, true))
            {
                throw new System.ArgumentException("bad base-64");
            }

            // Maybe we got lucky and allocated exactly enough output space.
            if (decoder.op == decoder.output.Length)
            {
                return decoder.output;
            }

            // Need to shorten the array, so allocate a new one of the
            // right size and copy.
            byte[] temp = new byte[decoder.op];
            Array.Copy(decoder.output, 0, temp, 0, decoder.op);
            return temp;
        }

        /// <summary>
        /// Base64-encode the given data and return a newly allocated
        /// String with the result.
        /// </summary>
        /// <param name="input"> the data to encode </param>
        /// <param name="flags"> controls certain features of the encoded output.
        ///              Passing {@code DEFAULT} results in output that
        ///              adheres to RFC 2045. </param>
        public static string encodeToString(byte[] input, int flags)
        {
            try
            {
                return StringHelperClass.NewString(encode(input, flags), "US-ASCII");
            }
            catch (Exception e)
            {
                // US-ASCII is guaranteed to be available.
                throw e;
            }
        }




        //  --------------------------------------------------------
        //  encoding
        //  --------------------------------------------------------

        /// <summary>
        /// Base64-encode the given data and return a newly allocated
        /// String with the result.
        /// </summary>
        /// <param name="input">  the data to encode </param>
        /// <param name="offset"> the position within the input array at which to
        ///               start </param>
        /// <param name="len">    the number of bytes of input to encode </param>
        /// <param name="flags">  controls certain features of the encoded output.
        ///               Passing {@code DEFAULT} results in output that
        ///               adheres to RFC 2045. </param>
        public static string encodeToString(byte[] input, int offset, int len, int flags)
        {
            try
            {
                return StringHelperClass.NewString(encode(input, offset, len, flags), "US-ASCII");
            }
            catch (Exception e)
            {
                // US-ASCII is guaranteed to be available.
                throw e;
            }
        }
        /// <summary>
        /// Base64-encode the given data and return a newly allocated
        /// byte[] with the result.
        /// </summary>
        /// <param name="input"> the data to encode </param>
        /// <param name="flags"> controls certain features of the encoded output.
        ///              Passing {@code DEFAULT} results in output that
        ///              adheres to RFC 2045. </param>
        public static byte[] encode(byte[] input, int flags)
        {
            return encode(input, 0, input.Length, flags);
        }

        /// <summary>
        /// Base64-encode the given data and return a newly allocated
        /// byte[] with the result.
        /// </summary>
        /// <param name="input">  the data to encode </param>
        /// <param name="offset"> the position within the input array at which to
        ///               start </param>
        /// <param name="len">    the number of bytes of input to encode </param>
        /// <param name="flags">  controls certain features of the encoded output.
        ///               Passing {@code DEFAULT} results in output that
        ///               adheres to RFC 2045. </param>
        public static byte[] encode(byte[] input, int offset, int len, int flags)
        {
            Encoder encoder = new Encoder(flags, null);

            // Compute the exact length of the array we will produce.
            int output_len = len / 3 * 4;

            // Account for the tail of the data and the padding bytes, if any.
            if (encoder.do_padding)
            {
                if (len % 3 > 0)
                {
                    output_len += 4;
                }
            }
            else
            {
                switch (len % 3)
                {
                    case 0:
                        break;
                    case 1:
                        output_len += 2;
                        break;
                    case 2:
                        output_len += 3;
                        break;
                }
            }

            // Account for the newlines, if any.
            if (encoder.do_newline && len > 0)
            {
                output_len += (((len - 1) / (3 * Encoder.LINE_GROUPS)) + 1) * (encoder.do_cr ? 2 : 1);
            }

            encoder.output = new byte[output_len];
            encoder.process(input, offset, len, true);

            Debug.Assert(encoder.op == output_len);

            return encoder.output;
        }

        /* package */
        internal abstract class Coder
        {
            public byte[] output;
            public int op;

            /// <summary>
            /// Encode/decode another block of input data.  this.output is
            /// provided by the caller, and must be big enough to hold all
            /// the coded data.  On exit, this.opwill be set to the length
            /// of the coded data.
            /// </summary>
            /// <param name="finish"> true if this is the final call to process for
            ///               this object.  Will finalize the coder state and
            ///               include any final bytes in the output. </param>
            /// <returns> true if the input so far is good; false if some
            /// error has been detected in the input stream.. </returns>
            public abstract bool process(byte[] input, int offset, int len, bool finish);

            /// <returns> the maximum number of bytes a call to process()
            /// could produce for the given number of input bytes.  This may
            /// be an overestimate. </returns>
            public abstract int maxOutputSize(int len);
        }

        /* package */
        internal class Decoder : Coder
        {
            /// <summary>
            /// Lookup table for turning bytes into their position in the
            /// Base64 alphabet.
            /// </summary>
            internal static readonly int[] DECODE = new int[] { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 };

            /// <summary>
            /// Decode lookup table for the "web safe" variant (RFC 3548
            /// sec. 4) where - and _ replace + and /.
            /// </summary>
            internal static readonly int[] DECODE_WEBSAFE = new int[] { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, 63, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 };

            /// <summary>
            /// Non-data values in the DECODE arrays.
            /// </summary>
            internal const int SKIP = -1;
            internal const int EQUALS = -2;
            internal readonly int[] alphabet;
            /// <summary>
            /// States 0-3 are reading through the next input tuple.
            /// State 4 is having read one '=' and expecting exactly
            /// one more.
            /// State 5 is expecting no more data or padding characters
            /// in the input.
            /// State 6 is the error state; an error has been detected
            /// in the input and no future input can "fix" it.
            /// </summary>
            internal int state; // state number (0 to 6)
            internal int value;

            public Decoder(int flags, byte[] output)
            {
                this.output = output;

                alphabet = ((flags & URL_SAFE) == 0) ? DECODE : DECODE_WEBSAFE;
                state = 0;
                value = 0;
            }

            /// <returns> an overestimate for the number of bytes {@code
            /// len} bytes could decode to. </returns>
            public override int maxOutputSize(int len)
            {
                return len * 3 / 4 + 10;
            }

            /// <summary>
            /// Decode another block of input data.
            /// </summary>
            /// <returns> true if the state machine is still healthy.  false if
            /// bad base-64 data has been detected in the input stream. </returns>
            public override bool process(byte[] input, int offset, int len, bool finish)
            {
                if (this.state == 6)
                {
                    return false;
                }

                int p = offset;
                len += offset;

                // Using local variables makes the decoder about 12%
                // faster than if we manipulate the member variables in
                // the loop.  (Even alphabet makes a measurable
                // difference, which is somewhat surprising to me since
                // the member variable is final.)
                int state = this.state;
                int value = this.value;
                int op = 0;
                //JAVA TO C# CONVERTER WARNING: The original Java variable was marked 'final':
                //ORIGINAL LINE: final byte[] output = this.output;
                byte[] output = this.output;
                //JAVA TO C# CONVERTER WARNING: The original Java variable was marked 'final':
                //ORIGINAL LINE: final int[] alphabet = this.alphabet;
                int[] alphabet = this.alphabet;

                while (p < len)
                {
                    // Try the fast path:  we're starting a new tuple and the
                    // next four bytes of the input stream are all data
                    // bytes.  This corresponds to going through states
                    // 0-1-2-3-0.  We expect to use this method for most of
                    // the data.
                    //
                    // If any of the next four bytes of input are non-data
                    // (whitespace, etc.), value will end up negative.  (All
                    // the non-data values in decode are small negative
                    // numbers, so shifting any of them up and or'ing them
                    // together will result in a value with its top bit set.)
                    //
                    // You can remove this whole block and the output should
                    // be the same, just slower.
                    if (state == 0)
                    {
                        while (p + 4 <= len && (value = ((alphabet[input[p] & 0xff] << 18) | (alphabet[input[p + 1] & 0xff] << 12) | (alphabet[input[p + 2] & 0xff] << 6) | (alphabet[input[p + 3] & 0xff]))) >= 0)
                        {
                            output[op + 2] = (byte)value;
                            output[op + 1] = (byte)(value >> 8);
                            output[op] = (byte)(value >> 16);
                            op += 3;
                            p += 4;
                        }
                        if (p >= len)
                        {
                            break;
                        }
                    }

                    // The fast path isn't available -- either we've read a
                    // partial tuple, or the next four input bytes aren't all
                    // data, or whatever.  Fall back to the slower state
                    // machine implementation.

                    int d = alphabet[input[p++] & 0xff];

                    switch (state)
                    {
                        case 0:
                            if (d >= 0)
                            {
                                value = d;
                                ++state;
                            }
                            else if (d != SKIP)
                            {
                                this.state = 6;
                                return false;
                            }
                            break;

                        case 1:
                            if (d >= 0)
                            {
                                value = (value << 6) | d;
                                ++state;
                            }
                            else if (d != SKIP)
                            {
                                this.state = 6;
                                return false;
                            }
                            break;

                        case 2:
                            if (d >= 0)
                            {
                                value = (value << 6) | d;
                                ++state;
                            }
                            else if (d == EQUALS)
                            {
                                // Emit the last (partial) output tuple;
                                // expect exactly one more padding character.
                                output[op++] = (byte)(value >> 4);
                                state = 4;
                            }
                            else if (d != SKIP)
                            {
                                this.state = 6;
                                return false;
                            }
                            break;

                        case 3:
                            if (d >= 0)
                            {
                                // Emit the output triple and return to state 0.
                                value = (value << 6) | d;
                                output[op + 2] = (byte)value;
                                output[op + 1] = (byte)(value >> 8);
                                output[op] = (byte)(value >> 16);
                                op += 3;
                                state = 0;
                            }
                            else if (d == EQUALS)
                            {
                                // Emit the last (partial) output tuple;
                                // expect no further data or padding characters.
                                output[op + 1] = (byte)(value >> 2);
                                output[op] = (byte)(value >> 10);
                                op += 2;
                                state = 5;
                            }
                            else if (d != SKIP)
                            {
                                this.state = 6;
                                return false;
                            }
                            break;

                        case 4:
                            if (d == EQUALS)
                            {
                                ++state;
                            }
                            else if (d != SKIP)
                            {
                                this.state = 6;
                                return false;
                            }
                            break;

                        case 5:
                            if (d != SKIP)
                            {
                                this.state = 6;
                                return false;
                            }
                            break;
                    }
                }

                if (!finish)
                {
                    // We're out of input, but a future call could provide
                    // more.
                    this.state = state;
                    this.value = value;
                    this.op = op;
                    return true;
                }

                // Done reading input.  Now figure out where we are left in
                // the state machine and finish up.

                switch (state)
                {
                    case 0:
                        // Output length is a multiple of three.  Fine.
                        break;
                    case 1:
                        // Read one extra input byte, which isn't enough to
                        // make another output byte.  Illegal.
                        this.state = 6;
                        return false;
                    case 2:
                        // Read two extra input bytes, enough to emit 1 more
                        // output byte.  Fine.
                        output[op++] = (byte)(value >> 4);
                        break;
                    case 3:
                        // Read three extra input bytes, enough to emit 2 more
                        // output bytes.  Fine.
                        output[op++] = (byte)(value >> 10);
                        output[op++] = (byte)(value >> 2);
                        break;
                    case 4:
                        // Read one padding '=' when we expected 2.  Illegal.
                        this.state = 6;
                        return false;
                    case 5:
                        // Read all the padding '='s we expected and no more.
                        // Fine.
                        break;
                }

                this.state = state;
                this.op = op;
                return true;
            }
        }

        /* package */
        internal class Encoder : Coder
        {
            /// <summary>
            /// Emit a new line every this many output tuples.  Corresponds to
            /// a 76-character line length (the maximum allowable according to
            /// <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>).
            /// </summary>
            public const int LINE_GROUPS = 19;

            /// <summary>
            /// Lookup table for turning Base64 alphabet positions (6 bits)
            /// into output bytes.
            /// </summary>
            internal static readonly byte[] ENCODE = new byte[] { (byte)'A', (byte)'B', (byte)'C', (byte)'D', (byte)'E', (byte)'F', (byte)'G', (byte)'H', (byte)'I', (byte)'J', (byte)'K', (byte)'L', (byte)'M', (byte)'N', (byte)'O', (byte)'P', (byte)'Q', (byte)'R', (byte)'S', (byte)'T', (byte)'U', (byte)'V', (byte)'W', (byte)'X', (byte)'Y', (byte)'Z', (byte)'a', (byte)'b', (byte)'c', (byte)'d', (byte)'e', (byte)'f', (byte)'g', (byte)'h', (byte)'i', (byte)'j', (byte)'k', (byte)'l', (byte)'m', (byte)'n', (byte)'o', (byte)'p', (byte)'q', (byte)'r', (byte)'s', (byte)'t', (byte)'u', (byte)'v', (byte)'w', (byte)'x', (byte)'y', (byte)'z', (byte)'0', (byte)'1', (byte)'2', (byte)'3', (byte)'4', (byte)'5', (byte)'6', (byte)'7', (byte)'8', (byte)'9', (byte)'+', (byte)'/' };

            /// <summary>
            /// Lookup table for turning Base64 alphabet positions (6 bits)
            /// into output bytes.
            /// </summary>
            internal static readonly byte[] ENCODE_WEBSAFE = new byte[] { (byte)'A', (byte)'B', (byte)'C', (byte)'D', (byte)'E', (byte)'F', (byte)'G', (byte)'H', (byte)'I', (byte)'J', (byte)'K', (byte)'L', (byte)'M', (byte)'N', (byte)'O', (byte)'P', (byte)'Q', (byte)'R', (byte)'S', (byte)'T', (byte)'U', (byte)'V', (byte)'W', (byte)'X', (byte)'Y', (byte)'Z', (byte)'a', (byte)'b', (byte)'c', (byte)'d', (byte)'e', (byte)'f', (byte)'g', (byte)'h', (byte)'i', (byte)'j', (byte)'k', (byte)'l', (byte)'m', (byte)'n', (byte)'o', (byte)'p', (byte)'q', (byte)'r', (byte)'s', (byte)'t', (byte)'u', (byte)'v', (byte)'w', (byte)'x', (byte)'y', (byte)'z', (byte)'0', (byte)'1', (byte)'2', (byte)'3', (byte)'4', (byte)'5', (byte)'6', (byte)'7', (byte)'8', (byte)'9', (byte)'-', (byte)'_' };
            public readonly bool do_padding;
            public readonly bool do_newline;
            public readonly bool do_cr;
            internal readonly byte[] tail;
            internal readonly byte[] alphabet;
            /* package */
            internal int tailLen;
            internal int count;

            public Encoder(int flags, byte[] output)
            {
                this.output = output;

                do_padding = (flags & NO_PADDING) == 0;
                do_newline = (flags & NO_WRAP) == 0;
                do_cr = (flags & CRLF) != 0;
                alphabet = ((flags & URL_SAFE) == 0) ? ENCODE : ENCODE_WEBSAFE;

                tail = new byte[2];
                tailLen = 0;

                count = do_newline ? LINE_GROUPS : -1;
            }

            /// <returns> an overestimate for the number of bytes {@code
            /// len} bytes could encode to. </returns>
            public override int maxOutputSize(int len)
            {
                return len * 8 / 5 + 10;
            }

            public override bool process(byte[] input, int offset, int len, bool finish)
            {
                // Using local variables makes the encoder about 9% faster.
                //JAVA TO C# CONVERTER WARNING: The original Java variable was marked 'final':
                //ORIGINAL LINE: final byte[] alphabet = this.alphabet;
                byte[] alphabet = this.alphabet;
                //JAVA TO C# CONVERTER WARNING: The original Java variable was marked 'final':
                //ORIGINAL LINE: final byte[] output = this.output;
                byte[] output = this.output;
                int op = 0;
                int count = this.count;

                int p = offset;
                len += offset;
                int v = -1;

                // First we need to concatenate the tail of the previous call
                // with any input bytes available now and see if we can empty
                // the tail.

                switch (tailLen)
                {
                    case 0:
                        // There was no tail.
                        break;

                    case 1:
                        if (p + 2 <= len)
                        {
                            // A 1-byte tail with at least 2 bytes of
                            // input available now.
                            v = ((tail[0] & 0xff) << 16) | ((input[p++] & 0xff) << 8) | (input[p++] & 0xff);
                            tailLen = 0;
                        }
                        ;
                        break;

                    case 2:
                        if (p + 1 <= len)
                        {
                            // A 2-byte tail with at least 1 byte of input.
                            v = ((tail[0] & 0xff) << 16) | ((tail[1] & 0xff) << 8) | (input[p++] & 0xff);
                            tailLen = 0;
                        }
                        break;
                }

                if (v != -1)
                {
                    output[op++] = alphabet[(v >> 18) & 0x3f];
                    output[op++] = alphabet[(v >> 12) & 0x3f];
                    output[op++] = alphabet[(v >> 6) & 0x3f];
                    output[op++] = alphabet[v & 0x3f];
                    if (--count == 0)
                    {
                        if (do_cr)
                        {
                            output[op++] = (byte)'\r';
                        }
                        output[op++] = (byte)'\n';
                        count = LINE_GROUPS;
                    }
                }

                // At this point either there is no tail, or there are fewer
                // than 3 bytes of input available.

                // The main loop, turning 3 input bytes into 4 output bytes on
                // each iteration.
                while (p + 3 <= len)
                {
                    v = ((input[p] & 0xff) << 16) | ((input[p + 1] & 0xff) << 8) | (input[p + 2] & 0xff);
                    output[op] = alphabet[(v >> 18) & 0x3f];
                    output[op + 1] = alphabet[(v >> 12) & 0x3f];
                    output[op + 2] = alphabet[(v >> 6) & 0x3f];
                    output[op + 3] = alphabet[v & 0x3f];
                    p += 3;
                    op += 4;
                    if (--count == 0)
                    {
                        if (do_cr)
                        {
                            output[op++] = (byte)'\r';
                        }
                        output[op++] = (byte)'\n';
                        count = LINE_GROUPS;
                    }
                }

                if (finish)
                {
                    // Finish up the tail of the input.  Note that we need to
                    // consume any bytes in tail before any bytes
                    // remaining in input; there should be at most two bytes
                    // total.

                    if (p - tailLen == len - 1)
                    {
                        int t = 0;
                        v = ((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 4;
                        tailLen -= t;
                        output[op++] = alphabet[(v >> 6) & 0x3f];
                        output[op++] = alphabet[v & 0x3f];
                        if (do_padding)
                        {
                            output[op++] = (byte)'=';
                            output[op++] = (byte)'=';
                        }
                        if (do_newline)
                        {
                            if (do_cr)
                            {
                                output[op++] = (byte)'\r';
                            }
                            output[op++] = (byte)'\n';
                        }
                    }
                    else if (p - tailLen == len - 2)
                    {
                        int t = 0;
                        v = (((tailLen > 1 ? tail[t++] : input[p++]) & 0xff) << 10) | (((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 2);
                        tailLen -= t;
                        output[op++] = alphabet[(v >> 12) & 0x3f];
                        output[op++] = alphabet[(v >> 6) & 0x3f];
                        output[op++] = alphabet[v & 0x3f];
                        if (do_padding)
                        {
                            output[op++] = (byte)'=';
                        }
                        if (do_newline)
                        {
                            if (do_cr)
                            {
                                output[op++] = (byte)'\r';
                            }
                            output[op++] = (byte)'\n';
                        }
                    }
                    else if (do_newline && op > 0 && count != LINE_GROUPS)
                    {
                        if (do_cr)
                        {
                            output[op++] = (byte)'\r';
                        }
                        output[op++] = (byte)'\n';
                    }

                    Debug.Assert(tailLen == 0);
                    Debug.Assert(p == len);
                }
                else
                {
                    // Save the leftovers in tail to be consumed on the next
                    // call to encodeInternal.

                    if (p == len - 1)
                    {
                        tail[tailLen++] = input[p];
                    }
                    else if (p == len - 2)
                    {
                        tail[tailLen++] = input[p];
                        tail[tailLen++] = input[p + 1];
                    }
                }

                this.op = op;
                this.count = count;

                return true;
            }
        }
    }
    // CHECKSTYLE:ON

}